In this part of the Appendix, we
introduce the effective entangling crosstalk error model for \(N\) -qubit MS gates, generalising [1]}. We recall that the procedure followed in [1]} was to relate an analytical expression of the MS-gate fidelity for the target GHZ-type state \(\mathcal {F}=1-\epsilon _{\rm MS}\) , including various sources of errors in the experiment, to the error rate \(p_{\rm MS}\)  of an effective multi-qubit quantum channel (e.g. depolarising channel). In this way, one gathers intuition about the contribution of physical error sources to the error rate of standard quantum channels typically used in a QEC context, which can then serve to develop more sophisticated models [3]}.
